Blasting devices



June 4, 1957 K. A. SMITH BLASTING DEVICES Filed July 13, 1954 INVENTORKennefi flsifiraaie 5m if;

BYZ M Quiz) Mm ATTORNEYS United ELASTING DEVKTES Application July 13,1954, Serial No. 44$,ii23

Claims priority, application Great Britain November 2, 1953 12 Claims.(Cl. Idle-25) The present invention relates to blasting devices of thekind in which a charge of a non-.detonating gas-producing composition,together with a suitable initiating means, is enclosed in a rigidcylindrical container provided with a closure member adapted to releasethe gases produced on reaction of said charge from the container at apredetermined pressure so that a blasting effect is produced in aborehole, the body of the container being sufliciently strong towithstand the pressure developed and being capable of rte-utilisation.

Such blasting devices are well-known and widely used for example in theproduction of lump coal. Normally the gas release member takes the formof a rupturable disc sealing ed the container from a venting head, whichis screwed 'to the container and thereby holds the rupturable disc inposition, the seal being made gas-tight by the provision of a resilientgasket on one or both sides of the disc. As the non-detonatinggas-producing charges, equimolecular mixtures of ammonium chloride andsodium nitrite, with a small proportion of alkaline stabiliser, such asmagnesium-oxide, have been widely used but other compositions havingsimilar properties can also be used. The initiation of the reaction ofthese charges, which can be effected at atmospheric pressures, isnormally achieved by a local heating element which is actuatedelectrically and it is customary to load these charges above-ground.Some non-detonating gas-producing charges, however, have the extremelyvaluable property, which renders them suitable for underground loadingeven in gassy atmospheres, in that their self-propagating decompositionrequires in addition to local heating a super-atmospheric pressure, andfor these it is desirable that the local heating arent element shouldproduce sutficient gas to. give the required 7 a pressure for thereaction of the charge to proceed quickly at a useful rate.

It is desirable to be able to fire blasting devices of the kind whereinthe charge requires a super-atmospheric pressure for self-propagatingdecomposition without having recourse to electricity since the use ofelectricity has certain inherent dangers, for example, in gassy mines.

According to the present invention the improved blasting device of thekind in which a charge of a non-detonatgas producing composition capableof self-sustained and selfepropagating gas. producing reaction whenmerely locally heated under super-atmospheric pressure together with alocal heating element is enclosed in a rigid cylindrical containerclosed or fitted with a gas-tight closure at one end and fitted at theother end with a venting head separated from the container by arupturable disc is characterised in that the local heating element hasactuating means responsive to fiuid'pressure and in that the containerat. the endwhich-is closed or fitted with a gas-tight closure permitssaid actuating means to be connected to an external source of fluidpressure.

When said fluid is a gas said actuating means permits the introductionand nonvreturn of gas into the container. On the other hand when saidfluid is a liquid said actuating means excludes the introduction ofliquid into the container. The local heating element should preferablythen be one which generates the necessary gas pressure to enable saidcharge to undergo a self sustained and self-propagating gas-producingreaction.

The embodiment of the invention in which an external source of gassupply is used to cause the required superatmospheric pressure in thecontainer has the advantage that said super-atmospheric pressure ismaintained in the container notwithstanding leakages and ensures thatthe sudden gas evolution from the self-propagating decomposition of thecharge will cause the bursting disc to rupture quickly.

The invention also consists in a local heating element for blastingdevices of the aforesaid kind comprising a heating charge and means forthe actuation thereof responsive to the application of fluid pressure. Apreferred form of local heating element comprises, in a sealedcontainer, a heating charge, a percussion cap positioned to initiate thereaction of said heating charge and a projectile positioned so that onthe application of fluid pressure the projectile fires said percussioncap. The heating charge in these local heating elements may be of agasproducing type or may be of a kind which reacts exothermically withthe evolution of substantially no gas. Suitable compositions includemixtures of antimony and potassium permanganate and mixtures of siliconwith an oxidising agent such as red lead. The amount of heating chargeis sufficient to evolve about -100 calories.

The rupturable disc and venting cap in the blasting devices of theinvention may be conventional, for example, the rupturable disc may beof mild steel or of a filled or unfilled synthetic resin such as Tufnol(registered trademark), a synthetic resin bonded paper product, adaptedto burst at a pressure of the order of 10 tons/sq. in.

The non-detonating gas-producing charge capable of a self-propagatinggas-producing reaction when locally heated under super-atmosphericpressure may be for example the ammonium nitrate compositions claimed inco-pending applications Nos. 388,841, now Patent No. 2,769,701., issuedNovember 6, 1956, and 408,102, filed February 4, 1954. It is preferredthat the charge should be in a pre-packaged form and it is alsopreferred that the local heating element be embedded in a suitablyshaped cavity at one end thereof. If desired furthermore the charge inpre-packed form can be a cylinder having a diameter to form a close fitin the rigid cylindrical container.

Although water under pressure may be used to actuate the actuating meansresponsive to fluid pressure of the local heating element in theblasting device of the invention it is preferred to use a gas as forexample compressed air. It is further preferred to use an inert gas, asfor example carbon dioxide or nitrogen gas. If air is used it is usuallynecessary to adjust the composition of the gas-producing charge. The gaspressure required to actuate the actuating means of the local heatingelement should preferably be of the order of the super-atmosphericpressure required in the container. To permit the charge to undergoself-propagating decomposition quickly at a useful rate this gaspressure may range from to 1 8001bs./sq. in. i

The following table gives the time interval between the application oflocal heating to 570 gramsof a gas-pro ducing charge consisting of 49 byweight ammonium nitrate, 34% by weight magnesium "and 17% by weightwoodflour in a cardboard container nitrate hexahydrate and the burstingof the rupturable disc for different gas pressures in the container of 3litres capacity of a blasting device .at the moment of application ofthe local heating.

The invention is illustrated with reference to the diagnammatic drawingsaccompanying the specification in which 1 is a high tensile steelcontainer, 2 is a venting 2 head, 3 is a mild steel disc adapted toyield at a predetermined pressure of the order of 15 tons/sq. in., 4 and.5 are gaskets and 6 is a firing head to which a flexible pressure tube7 is attached by means of the nipple 8. 9 is a conduit lea-ding from thenipple 8 to the 30 interior of the firing head 6, 10 is a ball valveheldv in position by the sleeve 11 in such a way that it acts as anon-return pressure valve, 12 is a gasket, 13 is a fireproofed cardboardcontainer for the main charge 14 and 15 is a local heating element inaccordance with. the invention. In Fig. 2 (which shows the details ofthe local heating element 15) 16 is a metal casing, 17 is a heatingcharge capable of evolving about 70 calories on reaction, 18 aresupports for a percussion cap 19, 20 is a metal projectile held inposition by the rubber tube 9 21 and the metal band 22 which is crimpedround the; rubber tube 21 so that .an appreciable pressure is re-iquired to dislodge the projectile 20 and cause it to strike thepercussion cap 19. To operate the local heating element 15 gas pressure,for ex'ample compressed air, within the range 100-1800 lbs./ sq. in. isapplied through the tube 7 and valve 10 whereupon the projectile 20fires the percussion cap 19 causing the reaction of heating charge 17 totake place. The heat thus formed ind-uces the reaction of the maincharge 14 and thus the 60 bursting of the disc 3.

.The invention is also illustrated by the following examples.

Example 1 A charge of 20 oz. of a non-detonating gas-producingcomposition consisting of 49% by weight ammonium nitrate, 34% by weightmagnesium nitrate hexahydrate and 17% by Weight woodflour in a cardboardcontainer into one end of which is inserted a safety igniter of the kindillustrated in Fig. 2 containing a heating charge consisting of 0.25 g.of a composition containing by weight antimony and by weight potassiumpermanganate is inserted into the pressure resistance steel container1.'

Carbon dioxide is introduced through tube valve 10 at a pressure of 650lbs/sq. in. by the sudden opening of a valve (not shown) in tube 7 andthis causes the projectile 20 to strike the percussion cap 19 and thusto initiate the reaction'of the heating charge 17 e and at the same timeto produce a pressure of about 650 lbs./sq. in. within thesteelcontainer '1 thereby to permit the charge 14 to undergo quicklyself-propagating decompositio'n'due to the heat evolved from'thereaction of the heating charge 17. The time interval betweentheiconnectingof the steel container 1 to the supply of 7 and carbondioxide by the sudden opening of the valve (not shown) in tube 7 and therupturing of the bursting disc 3 is 4 seconds.

Example 2 If instead of carbon dioxide, nitrogen at 1,000 lbs/sq. in. isused in the same manner as in Example 1 to cause the projectile 20 tostrike the percussion cap 19 and to produce a pressure of about 1000lbs/sq. in.

10 in the steel container 1 the time interval between the connecting ofthe steel container 1 to the supply of nitrogen by the sudden opening ofthe valve (not shown) in tube 7 and the rupturing of the bursting disc 3is 2 seconds.

What I claim is:

1. A blasting device comprising a rigid hollow container, a charge ofnon-detonating, gas-producing composition capable of' self-sustained andself-propagating gas-producing reaction only when locally heated under asuper-atmospheric pressure disposed within said rigid container, a localheating element contained within said rigid container,pressure-responsive means for actuating said heating element, andgas-tight closures sealing both ends of said container, one of saidclosures being provided with means providing gas under pressure tooperate the actuating means of the local heating element and to subjectthe charge to said super-atmospheric pressure.

2. A blasting device as defined in claim 1 wherein the other of said endclosures comprises a rupturable member and a venting head separated fromthe interior of the container by said rupturable member.

3. A blasting device as defined in claim 1, wherein said gas-producingcomposition and said heating element are unitarily packaged so as tooffer no eflective resistance to the entry of gas under pressure intosaid container.

4. A blasting device as defined in claim 3, wherein said heating elementis embedded in one end of said gasproducing composition charge.

5. A blasting device as defined in claim 1, in which said heatingelement comprises a pressure-operated striker, a percussion cappositioned for actuation by said striker and a heating charge positionedfor initiation by said percussion cap.

6. A blasting device as defined in claim 5, wherein said striker ispartially exposed for actuation by entry of compressed gas into saidcontainer. 7. A blasting device as defined in claim 1, wherein saidgas-providing means comprises 'a one-way valve which is interposedbetween said container and an' external source of gas under pressure.

8. A blasting device as defined in claim 1, wherein the gas pressureutilized to operate the actuating means of the heating element isapproximately equal to the super-atmosphericpressure required toinitiate the chemical reaction of the gas-producing composition.

9. A blasting device as defined in claim 1, wherein the gas pressurerequired in the container to enable said 0 charge to undergoself-propagating decomposition ranges from to 1800 pounds'per squareinch.

10. A blasting device as defined in claim 1, wherein said charge ofgas-producing composition comprises at least one of the hydratednitrates of metals of low atomic weight of the group magnesium nitrate'hexahydrate and aluminum nitrate nonahydrate, and anon-explosive organicfuel consisting substantially of a dried vegetable carbohydratematerial, wherein the number of moles of combined water in the metalnitrate per mole of ammonium nitrate lies between 1 and 3 and whereinthe proportion of the organic fuel in the pulverulent mixture is suchthat the gases from the charge and said heating 7 element consist at thebursting pressure of said blasting device substantially of steam, carbondioxide and nitrogen.

11. A blasting device as defined in claim 1, wherein References Cited inthe file of this patent UNITED STATES PATENTS Hart Mar. 12, 1929 LawsonMay 3, 1932 Taylor June 30, 1936 Wright et a1. Jan. 29, 1952 SwansonSept. 22, 1953

